Area control insert for maintaining air flow uniformity around the combustor of a gas turbine engine

ABSTRACT

Means for improving flow uniformity and reducing disturbances in compressor discharge air flowing through passages around the combustion chamber of a gas turbine engine are provided by an area control insert. The insert comprises circumferentially and longitudinally extending walls within the forward portions of the air passages to constrict the cross-sectional areas of the passages. Such constriction operates to minimize pressure gradients within the turning and splitting air flow and thereby reduce the tendency for the air flow to separate from the passage walls at random locations around the periphery thereof.

11 States l Cohen et al. rug. '7, W73

[ AREA CONTROL INSERT FOR 3,364,678 1/1968 Alford 60/39.65 MAINTAININGAIR FLOW UNHFQRMWY 3,383,855 5/1968 Freeman et al.... 60/39.65 3,372,5423/1968 Sevetz 60/3936 AROUND THE COMBUSTOR A GAS 3,049,882 8/1962LaBastie et a].... 60/39.65 TURBINE ENGINE 3,58l,492 6/197] Norgren etal 60/3936 75 Inventors; Joseph David Cohen Danvers; Neil 3,589,1276/1971 Kenworthy et al. 60/39.65

Roger Brookes, Topsfield; Herbert Carl Stark, West Peabody; RobertHirschkron, Marblehead; Gerald William Lawson, Boxford, all of Mass.

[73] Assignee: General Electric Company, Lynn,

Mass.

[22] 6 Filed: Mar. 1, 1972 [2l] Appl. No.: 230,839

[52] U.S. Cl. 60/3936, 60/39.65

[51] Int. (II. lFtlZc 7/18 [58] Field of Search ..60/39.36, 39.65

[56] References Cited UNITED STATES PATENTS 3,631,674 Ill 972 Taylor60/3936 Primary Examiner--Carlton R. Croyle Assistant Examiner-WarrenOlsen Attorney-Edward S. Roman et al.

57 ABSTRACT Means for improving flow uniformity and reducingdisturbances in compressor discharge air flowing through passages aroundthe combustion chamber of a gas turbine engine are provided by an areacontrol insert. The insert comprises circumferentially andlongitudinally extending walls within the forward portions of the airpassages to constrict the cross-sectional areas of the passages. Suchconstriction operates to minimize pressure gradients within the turningand splitting air flow and thereby reduce the tendency for the air flowto separate from the passage walls at random locations around theperiphery thereof.

1 Claim, 3 Drawing Figures PATENTEU AUG 71975 BACKGROUND OF THEINVENTION This invention relates generally to an area control insert formaintaining air flow uniformly around the combustion chamber of a gasturbine engine, and more particularly to an area control insert forminimizing pressure gradients and reducing random flow separation fromthe walls of the flow passages around the combustion chamber of a gasturbine engine.

It is common in the gast turbine art to continuously strive for improvedversions of well established engine designs. Such engines, generallyreferred to as growth engines, may in one form have increased thrust andefficiency provided by an increased maximum operating temperature.Increased temperatures can be made possible through the introduction ofimproved alloys within the turbine stage or through redesign of theturbine cooling mechanism. For such growth engines it is often desirablethat the original combustion design be retained, thereby avoiding theexpense and time consumed in redesigning and retooling to manufacture anentirely new combuster.

Gas turbine combustion apparatus generally includes a combustion chambersurrounded by spaced apart inner and outer casings, which, incooperation with the combustion chamber, define inner and outer passagesrespectively. Air flow from a gas turbine compressor is divided, with aportion circulated through the combustion chamber. The remainder of theair is circulated through the inner and outer passages around thecombustion chamber. The air then enters the combustion chamber throughopenings in a combustion liner so as to both support combustion andreduce the temperature of the hot gases of combustion before they aredirected to a turbine.

The forward ends of the inner and outer air flow passages are quitegenerally divergent and effect a reduction in velocity of the air flowas it enters the area of the combustor apparatus. Due to the air flowvelocity decrease through the initial divergent portions of the passagesit is often difficult to predict the exact nature of the pressuregradients within the flow field. Nonuniform pressure gradients can causethe air flow to separate at random locations particularly along theinner casing of the inner passage. Such random flow separationprecipitates a non-uniform flow field within the passages and is anundesirable condition, particularly at the increased operatingtemperatures of a growth type of engine. The non-uniform flow field canlead to overheating of the liner in streaked areas along the length ofthe liner. Such localized overheating will often lead to a deteriorationof the liner which upon routine inspection is genrally first manifest bya visible streaked discoloration of the liner commonly referred to ashot streaking. The localized overheating caused by random flowseparation can extend the length of the liner into the turbine alsocausing deterioration of the turbine.

Any combustion apparatus for a gas turbine engine may have a limiteddegree of random flow separation within its inner and outer passages,but hot streaking may not be a significant problem because the operatingtemperature of the combustor is sufficiently low that thenon-uniform'flow field still provides for adequate performance. However,a growth version of the same engine may call for a significantlyincreased operating temperature. whereupon hot streaking may suddenlymanifest itself as a significant problem which, if uncorrected, willlead to rapid deterioration of the combustor and turbine hardward andreduced intervals between replacement.

I-Ieretofore, the designer had no choice, in such a case, but tocompletely redesign the combustor apparatus which involves substantialadditional time, together with materially increased cost. Suchadditional time and expenditure increases the overall cost for thegrowth version of an engine, making it substantially less attractive.

Therefore, it is an object of this invention to rovide a simple andeconomical means by which the air flield uniformity in the combustionapparatus of agrowth type of engine might be optimized withoutcompletely redesigning the combustor.

It is also an object of this invention to provide a simple andeconomical means of preventing hot streaking and rapid deterioration ofthe combustor and turbine in growth types of engines where the operatingtemperatures have been substantially increased.

It is a further object of this invention to provide a simple andeconomical means for minimizing random air flow separation from the airpassage casings so as to permit an increased engine operatingtemperature.

SUMMARY OF THE INVENTION Gas turbine combustion apparatus of the typsuitable for inclusion of the means of this invention generally includesa combustion chamber mad up of spaced apart inner and outer annularliners. Inner and outer cowl portions extend from the forward ends ofthe respective liners and converge together to form a flow divider. Anouter wall or casing spaced apart from the outer liner and cowl definesan outer air flow passage therebetween, and an inner wall or casingspaced apart from the inner liner and cowl defines an inner air flowpassage therebetween. The means of this invention for providing improvedair flow field uniformity includes an area control insert comprisingcircumferentially and longitudinally extending walls attached to a cowlportion, wherein the major inside surface of the wall is spaced apartfrom the cow] portion so as to constrict the effective cross-sectionalarea of the forward portion of the flow passage, thereby preserving thehigh velocity character of the flow and minimizing the tendency for theair flow to separate from the walls of the flow passages at randomlocations.

DESCRIPTION OF THE DRAWINGS While the secification concludes with claimsdistinctly claiming and particularly pointing out the inventiondescribed'herein, it is believed that the invention will be more readily understood by reference to e discussion below and the accompanyingdrawings in which:

FIG. l is a partly cutaway side view of a gas turbine engine embodyingthe combustion apparatus of this invention.

FIG. 2 is an enlarged cross-sectinal view of the combustion apparatus ofFIG. 1 showing the means of this invention for reducing random air flowseparation from the walls of the air flow passages.

FIG. 3 is a partial perspective view of the combustion apparatus of FIG.2 as viewed from the bottom of the engine showing the means of thisinvention for reducing random air flow separation from the walls of theflow passages.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring specifically to FIG.1, there is shown generally at a gas turbine engine of the well knownturbojet variety. While this is used as an example to illustrate theinvention, it will be appreciated that the invention has application toany apparatus utilizing a continuous fluid flow combustion system; forexample, aircraft turbofan or land-based combustion engines. In anyevent, as shown in FIG. 1, the gas turbine engine 10 includes an outerhousing 12 having an inlet end 13, receiving air which enters acompressor 14 which may be of the multistage axial flow type having rowsof rotor blades 16. interspersed with the rotor blades are rows ofstator blades 18 which are affixed at one end to the inner surface ofthe housing 12. At the downstream end of the compressor 14 is a row ofcompressor outlet guide vanes 19, followed by an annular diffuserpassage or compressor discharge passage indicated generally at 20.

The diffuser discharges the pressurized air into a combustor indicatedgenerally at 22 from whence the heated gases exit at high velocitythrough the power turbine 24. The power turbine extracts work to drivethe compressor 14 by means of connecting shaft 34 on which bothcomponents are mounted. The rotating compressorturbine set is mounted inthe engine by suitable bearing means. The hot gas stream leaving theturbine is discharged to atmosphere to provide thrust through an exhaustnozzle which may be of the adjustable type as shown at 28.

Referring now to the enlarged view of FIG. 2, it will be seen that thecombustor comprises an outer casing wall, indicated generally at 30, andan inner casing wall, indicated generally at 32. The outer and innerwalls are radially spaced from a pair of outer and inner combustionchamber liners, indicated generally at 34 and 36 respectively. Thecombustion liners are appropriately supported in the combustor by aplurality of radially extending and circumferentially spaced struts oneof which is shown at 33. The liners 34, 36 are interconnected at theirforward ends by an annular transverse wall or dome 38 having a pluralityof louvers 39 therethrough to accommodate the flow of pressurized airinto the combustion chamber 37. Intermediate the radially spaced ends ofdome 38 there is a plurality of circumferentially spaced openings ofwhich only one is shown at 40. The openings 40 are adapted to receivefuel nozzles 42 which are supplied through conduit 43 with fuel tosupport combustion. Suitable ignition means such as the ignitcr 44 areprovided in order to initiate combustion.

The combustor walls 30, 32 and liners 34, 36 cooperate to define threeconcentric annular flow paths into which air from the compressor issplit. The forward ends of the liners 34, 36 have cowl portions 340, 36aresptectively, which converge into an annular edge 45 so as to split theflow into two streams. A plurality of circumferentially spaced openings46, which may best be viewed in FIG. 3, are disposed around the forwardedge 45 of the cowl portions 340, 36a and provide for the entrance of acompressed stream of air into the combustion chamber 37 defined by theseliners. Additional compressed air is admitted to the combustion chamberthrough the circumferentially extending openings 47. Strut 33, which isillustrated in FIG. 3 partially in phantom, has a generally teardropcrosssection an intersects the converging cowl portions 34a, 360 at thegenerally V shaped cut 48. The forward ends of the combustor walls alsohave mutually convergent portions 30a, 32a and are joined to the ends ofthe diffuser 30 walls.

The combustor wall 30 and liner 34 define an outer cooling flow passageand the liner 36 and com bustor wall 32 definean ir ner coolingflgwpassage 52 wherein both passages are first divergent frbriith diffuserflow path and then curve to the longitudinally extending downwstreamportions of the liners. The inner and outer flow passages 50, 52 provideair for cooling the combustor walls as well as supplying additionaldilution air through liner openings 54 downstream of the nozzle 42 formixing with cooling the combustion gases before they reach the turbine.

Air flow through the initial divergent portions of the flow passages 50,52 is often difficult to predict and may precipitate random flowseparation from the combustor walls 30, 32. Random separation of the airflow from the walls of the liner disturbs the uniformity of the flowfield, precipitating hot streaking along the combustion liner whichmaterially shortens the-effective life of the liner and turbine. Aspreviously discussed, this problem is particularly acute with so-calledgrowth en gines where increased combustor temperatures may cause rapiddeterioration of the liners and turbine in cases where the combustionapparatus had not previously been designed for optimum flow fielduniformity. However, it should be remembered that the original combustordesign may well have been entirely satisfactory of operation within theoriginal temperature range, and it is only th increased operatingtemperatures of the gtowth engine which suddenly precipitate the latentproblem of hot streaking Confronted with this problem, the designerheretofore had no choice but to implement a time consuming and costlyredesign of the entire combustor apparatus resulting in a substantiallymore expensive growth engine, and this was in effect, what happened foryears prior to our invention. However, we have found that the device ofthis invention can simply and economically overcome the necessity for anentirely new combustor design.

Referring now to both FIG. 2 and FIG. 3, there is illustrated a typicalcombustor where hot streaking might exist particularly in the areaadjacent the inner cowl portion 366a. During engine operation, airdelivered from the compressor 14 through the compressor outlet guidevanes 19 become spit by the converging areas of the cowl portions 340and 36a. The gas stream from the diffuser passage 20 is turned outwardlyby the outer flow passage 50 and inwardly by the inner flow passage 52.Rapid increase in area within the flow passages 50, 52 cause a reductionin the velocity of the air flowing therethrough, thereby resulting in adecrease in the pressure of the air flowing within thepassage 50, 52. Ascan be readily seen from the drawing, for the particular engine designshown, the portion 32a of the inside combustor casing wall 32 divergesmore rapidly than the portion 30a of the outside combustor casing wall22. This rapid divergence of the inside wall 32, particularly in theareas adjacent the inner cowl portion 360, can lead to severe randomflow separation from the combustion liner resulting in severe hotstreaking with the combustion chamber.

The are control insert of this invention minimizes the flow separationand attendant hot streaking of the combustion chamber in a simple andeconomical manner without necessitating the entire redesign of thecombustion liner. The area control insert is shown in the drawings ascomprising a circumferentially and longitudinally extending wall showngenerally at 60 and including a major inner surface 62 maintainedradially inward of the inner cowl portion 36a so as to constrict theeffective cross-sectional area of the forward portion of the inner flowpassage. The forward end of the wall 60 is preferably flared in agenerally outward radial direction into theinner cowl portion 36a asindicated at 64 in order to maintain a smooth and uniform streamlinedair flow over the forward edge of the wall 60. The aft end of the wall60 terminates in a blunt edge 66 which operates in the manner ofa stepdiffuser causing a rapid uniform expansion of the flow field passing thethereover. [t is preferred that the wall 60 be segmented into discretearcuate sectins as best shown in FIG. 3 in order to better facilitateinstallation. Also, the wall 60 may be made of the same material as thecowl and can be welded to the cow] in a manner well known to the art.

While the inventors do not intend to be bound by any particular theoryof operation, it is believed that the unusual benefits and advantagesattributable to inclusion of the are control insert may be explained asfollows. Random air flow separation and the attendant hot streaking ofthe combustion chamber are minimized by the wall 60 in the followingmanner. The tendency for the air flow to diffuse upon initial entry intothe flow passage 52 is substantially reduced passage 52 in that portionadjacent the inner cowl 36a. Decreasing the cross-sectional area of theflow path preserves the high velocity character of the flow around thinner wall portion 32a minimizing pressure gradients and effectingminimal separation of flow from the interior surface of the wall portion32a, thus minimizing hot streaking. The blunt edge 66 at the aft end ofthe wall 60 rapidly diffuses the flow causing a uniform reduction in thevelocity of air flowing therethrough, together with a uniform increasein the static pressure of the flow within the cooling passages. The flowreattaches to the inner cowl surface 36a causing a uniformly reducedvelocity flow field to flow over the cooling liner 36 and through theliner openings 54. This sudden uniform reduction in velocity andincrease in pressure in the area of the cooling passages immediatelyupstream of the liner openings 54 inhibits hot streaking and failitatesflow mixing with only a slight pressure drop between the passage 52 andthe interior of the combustion chamber 37, thereby promotoing greateruniformity of the flow field without additional pressure loss.

Of secondary advantage is the effect that the turbulence immediately aftof the blunt edge 66 has in breaking up the wake behind the strut 33. Ifthe wake behind strut 33 were left undisturbed, there would be adistinct tendency to develop hot streaking in this area.

As has been made readily apparent, the above described wall is ofparticular advantage for increasing the operating temperatures ofestablished engines which might not have been designed for optimum flowfield uniformity due to the difficulty in intially predicting the airflow through the divergent portions of the flow passages. Economy andsimplicity make the device most attractive particularly for thosesituations where the only alternative would necessitate a costlyredesign of the entire combustion apparatus.

While only one preferred embodiment of the above described device hasbeen shown and described, it

should be ovbious that certain changes could be made in the describedembodiment without departing from the broader aspects of the invention.For example, if hot streaking had been experienced due to flowseparation in the outer cooling flow passage, then wall 60 could havebeen attached to the outer cowl portion with equal success. Therefore,in light of the above, it is intended that the appended claims'cover allsuch changes and modifications as fall within the broader conepts of theabove disclosure.

Having thus described one embodiment of the inven tion, what is desiredto be secured by letters patent is as follows:

1. In a gas turbine engine of the type having a combustion apparatuswhich includes spaced apart inner and outer annular liners defining acombustion chamber therebetween, inner and outer converging cowlportions extending from the forward ends of the respective linerswherein the inner cowl portion diverges more rapidly than the outer cowlprotion, an outer wall spaced apart from the outer liner and cowldefining an outer flow passage therebetween and an inner wall spacedapart from the inner liner and cowl defining an inner flow passagetherebetween, improved flow field uniformity is provided by an areacontrol insert comprising:

a circumferentialy and longitudinally extending wall having a pluralityof circumferentially spaced, arcuate segments attached to the inner cowlportion wherein; the major inside surface of the segmented wall isspaced apart from the inner cowl portion so as to constrict theeffective cross-sectional area of the forward portion of the inner flowpassage, the forward end of the segmented wall is preferably flared inan outward direction into the 9nner cowl portion in order to maintain asmooth and uniform streamlined flow field over the forward edgeof thewall, and the aft end of the wall termintates in a blunt edge so as toprovide for the rapid uniform diffusion of air flow passing thereover,thereby pro viding a uniformly reduced velocity flow field whichminimizes the tendency for the air flow to separate from the inner linerat random locations.

K t t t

1. In a gas turbine engine of the type having a combustion apparatuswhich includes spaced apart inner and outer annular liners defining acombustion chamber therebetween, inner and outer converging cowlportions extending from the forward ends of the respective linerswherein the inner cowl portion diverges more rapidly than the outer cowlportion, an outer wall spaced apart from the outer liner and cowldefining an outer flow passage thErebetween and an inner wall spacedapart from the inner liner and cowl defining an inner flow passagetherebetween, improved flow field uniformity is provided by an areacontrol insert comprising: a circumferentially and longitudinallyextending wall having a plurality of circumferentially spaced, arcuatesegments attached to the inner cowl portion wherein; the major insidesurface of the segmented wall is spaced apart from the inner cowlportion so as to constrict the effective cross-sectional area of theforward portion of the inner flow passage, the forward end of thesegmented wall is preferably flared in an outward direction into theinner cowl portion in order to maintain a smooth and uniform streamlinedflow field over the forward edge of the wall, and the aft end of thewall terminates in a blunt edge so as to provide for the rapid uniformdiffusion of air flow passing thereover, thereby providing a uniformlyreduced velocity flow field which minimizes the tendency for the airflow to separate from the inner liner at random locations.